
DocID024597 Rev 5
725/1830
RM0351
Digital filter for sigma delta modulators (DFSDM)
756
Signed data format in registers
: Data is in a signed format in registers for final output data,
analog watchdog, extremes detector, offset correction. The msb of output data word
represents the sign of value (two’s complement format).
24.4.15 Launching
conversions
Injected conversions
can be launched using the following methods:
•
Software: writing ‘1’ to JSWSTART in the DFSDM_FLTxCR1 register.
•
Trigger: JEXTSEL[2:0] selects the trigger signal while JEXTEN activates the trigger
and selects the active edge at the same time (see the DFSDM_FLTxCR1 register).
•
Synchronous with DFSDM_FLT0 if JSYNC=1: for DFSDM_FLTx (x>0), an injected
conversion is automatically launched when in DFSDM_FLT0; the injected conversion is
started by software (JSWSTART=1 in DFSDM_FLT0CR2 register). Each injected
conversion in DFSDM_FLTx (x>0) is always executed according to its local
configuration settings (JSCAN, JCHG, etc.).
If the scan conversion is enabled (bit JSCAN=1) then, each time an injected conversion is
triggered, all of the selected channels in the injected group (JCHG[7:0] bits in
DFSDM_FLTxJCHGR register) are converted sequentially, starting with the lowest channel
(channel 0, if selected).
If the scan conversion is disabled (bit JSCAN=0) then, each time an injected conversion is
triggered, only one of the selected channels in the injected group (JCHG[7:0] bits in
DFSDM_FLTxJCHGR register) is converted and the channel selection is then moved to the
next selected channel. Writing to the JCHG[7:0] bits when JSCAN=0 sets the channel
selection to the lowest selected injected channel.
Only one injected conversion can be ongoing at a given time. Thus, any request to launch
an injected conversion is ignored if another request for an injected conversion has already
been issued but not yet completed.
Regular conversions
can be launched using the following methods:
•
Software: by writing ‘1’ to RSWSTART in the DFSDM_FLTxCR1 register.
•
Synchronous with DFSDM_FLT0 if RSYNC=1: for DFSDM_FLTx (x>0), a regular
conversion is automatically launched when in DFSDM_FLT0; a regular conversion is
started by software (RSWSTART=1 in DFSDM_FLT0CR2 register). Each regular
conversion in DFSDM_FLTx (x>0) is always executed according to its local
configuration settings (RCONT, RCH, etc.).
Only one regular conversion can be pending or ongoing at a given time. Thus, any request
to launch a regular conversion is ignored if another request for a regular conversion has
already been issued but not yet completed. A regular conversion can be pending if it was
interrupted by an injected conversion or if it was started while an injected conversion was in
progress. This pending regular conversion is then delayed and is performed when all
injected conversion are finished. Any delayed regular conversion is signalized by RPEND bit
in DFSDM_FLTxRDATAR register.
24.4.16 Continuous and fast continuous modes
Setting RCONT in the DFSDM_FLTxCR1 register causes regular conversions to execute in
continuous mode. RCONT=1 means that the channel selected by RCH[2:0] is converted
repeatedly after ‘1’ is written to RSWSTART.